Fluid delivery system

ABSTRACT

A high pressure fluid delivery system is disclosed in which two or more guns, each having a high pressure nozzle outlet and a low pressure dump outlet, may be connected to and operated from the same pump. Pressure responsive control apparatus is provided in the flow line between each gun and the pump and each such apparatus includes a valve responsive to the fluid pressure at its respective gun for directing fluid either directly to such gun when flow is through the gun nozzle, or through an opening through the valve substantially the same size as the nozzle orifice of such gun when the gun is dumping.

[ 51 Aug. 27, 1974 FLUID DELIVERY SYSTEM [75] Inventor: Amos Pacht, Houston, Tex.

[73] Assignee: Partek Corporation of Houston, Houston, Tex.

[22] Filed: Aug. 17, 1973 [21] App]. No.: 389,244

3,672,575 6/1972 Hinrichs 239/447 Primary ExaminerL1oyd L. King Assistant ExaminerAndres Kashnikow Attorney, Agent, or Firm-Hubbard, Thurman, Turner & Tucker [57] ABSTRACT A high pressure fluid delivery system is disclosed in which two or more guns, each having a high pressure nozzle outlet and a low pressure dump outlet, may be connected to and operated from the same pump. Pressure responsive control apparatus is provided in the flow line between each gun and the pump and each such apparatus includes a valve responsive to the fluid pressure at its respective gun for directing fluid either directly to such gun when flow is through the gun nozzle, or through an opening through the valve substantially the same size as the nozzle: orifice of such gun when the gun is dumping.

13 Claims, 11 Drawing Figures EAIENIEDIUSZ'HBH sum ear :2

1 FLUID DELIVERY SYSTEM This invention relates to a high pressure fluid delivery system and in one of its aspects to pressure control apparatus for providing substantially constant pressures from a pump delivery fluid to the system.

In the prior art, fluid systems are provided in which a high pressure stream of water, i.e., at pressures of 6,000 10,000 pounds or more, are used for many cleaning applications. In these systems one or more hand-held valve assemblies or guns are provided, and are connected by a hose to a common outlet of a pump. The guns generally include a housing having a valve therein, a barrel extension for directing the high pressure stream of water through a nozzle to the object to be cleaned, a handle or trigger mechanism for operating the valve, and a relatively unrestricted pressure relief or dump outlet for relieving pressure in the assembly when flow through the high pressure nozzle outlet is interrupted by operation of the valve. When the gun is dumping water, pressures are generally no more than a few hundred pounds, and a sudden reduction on the load or the pump occurs.

Because of the wide differential between water pressures when water is dumped and when it is being discharged through the gun nozzle, apparatus have been suggested for automatically decreasing the pump engine speed during dumping, such as shown in US. Pat. No. 3,335,962. However, where two or more nozzle guns are employed in random operation, such apparatus is generally not practical. When two or more guns are used from a single source, it is highly desirable that a constant inlet pressure to the guns be provided independent of the operation of the guns. In US. Pat. No. 3,375,980, a system is provided where when a nozzle gun is not discharging high pressure fluid, the fluid is passed through an orifice that was substantially the same size as the guns nozzle orifice. Thus, whether a gun is discharging through its nozzle or not, a substantially constant pressure is provided by the pump. However, this system requires the use of a separate source of compressed air, a diaphragm valve assembly for each gun for switching between the gun and the added orifice, pneumatic control means on each gun for operating the diaphragm valve, and a considerable amount of additional piping. The addition of the additional pneumatic system thus represents a substantial added expense, a source of frequent maintenance and leakage problems, and generally unduly complicates the fluid delivery system. Also, the guns employed are of special design and are not dump" guns which are readily available and generally preferred since the operator is always assured that the high pressure is being relieved.

ln co-pending US. Pat. application Ser. No. 297,216, filed Oct. 13, 1972, now US. Pat. No. 3,765,607 and assigned to the assignee of this application, a fluid delivery system is disclosed which solves substantially all of the problems enumerated with respect to the prior art by providing a control apparatus connected between each nozzle gun of the fluid delivery system and the pump. Fluid flow through the central apparatus is either through a main passageway, which includes a pressure responsive valve, or a by-pass passageway, which includes an orifice substantially the same size of the nozzle orifice of the gun connected to the respective control apparatus. When the pressure at the inlet of the gun is high, such as when the gun is actuated to provide a high pressure discharge, the valve in the main passageway is open to permit relative unrestricted flow through the passageway. However, when the gun is dumping so that the fluid pressure at the inlet of the gun is relatively low, the valve in the main passageway is closed and flow will be through the relatively restricted by-pass passageway to simulate the effect of the gun on the pumping system. In this manner, a substantially constant pressure is maintained on the pump even though two or more nozzle guns are connected to it and used at different times.

While the system just described is highly satisfactory, it requires the machining of two separate passageways in a housing, and is not as satisfactory for higher fluid flow rates as it is for lower rates of flow. It is thus the primary object of this invention to provide control apparatus of the kind described for use in a high pressure fluid delivery system in which two or more dump guns of standard design may be supplied fluid by a single pump and in which a substantially constant pressure is provided by the pump during dumping operation of any of the guns.

Another object of this invention is to provide such control apparatus which may be machined with a single flow passageway.

Another object of this invention is to provide such a control apparatus which is suitable for use with higher rates of fluid flow than similar such control apparatus previously provided.

Another object of this invention is to provide such a control apparatus in which a simple adjustment can be made to accommodate different flow conditions, or to accommodate guns of different orifice size.

Another object of this invention is to provide such a control apparatus in which the above objects can be accomplished without the need for the addition of relatively expensive, complicated or large components.

These and other objects of this invention, which will be apparent upon consideration of the appended drawings and claims, and the following detailed description, are accomplished by providing a fluid pressure control apparatus between each gun of a fluid discharge system and the pump of the system for maintaining a substantially constant load on the pump. Each such control apparatus includes a flow passageway having a valve therein, and in one embodiment an orifice in the valve sized to provide substantially the same pressure drop across the control apparatus, which is generally the same size orifice as the discharge orifice of the gun connected to the control apparatus. The valve is responsive to the pressure of fluid flowing to the gun connected to the control apparatus and when the gun is discharging fluid at a high pressure through its nozzle, the valve is open. However, when the gun is dumping, the valve in the respective control apparatus responds to the changes in pressure at the outlet of said control apparatus to close the flow passageway and direct fluid through the orifice in the valve. ln the preferred embodiments illustrated the valve is biased closed by a spring and means is provided for adjusting the compression of the spring to permit the valve to operate with pumps of different flow rates.

In another-embodiment of this invention, the valve means includes a stop to prevent it from being fully closed, so that the opening through it when it is against the stop is of a size to provide the required pressure drop. If desired, means can be provided for adjusting the size of the minimum opening to accommodate different flow conditions on different sizes of gun orifices.

One or more of the described control apparatus for controlling one or more nozzle guns can be provided in line with a single hose coming from a pump, so that when the pump is located at the same distance from the guns, only one main hose need be provided for a substantial part of this distance.

In the drawings, wherein like reference numerals are used throughout to designate like parts, and wherein preferred embodiments of this invention are illustrated,

FIG. 1 is a view in elevation of a fluid delivery system of this invention;

FIG. 2 is a sectional view taken at 2-2 in FIG. 1 illustrating one form of the control apparatus of this invention;

FIG. 3 is a view similar to FIG. 2 but with the valve means open;

FIG. 4 is a view similar to FIG. 2 but with an alternate arrangement of the valve means;

FIG. 5 is a view similar to FIG. 4 but with the valve means open;

FIG. 6 is an end view taken at 6-6 in FIG. 1;

FIG. 7 is a sectional view taken at 7--7 in FIG. 2;

FIG. 8 is a sectional view taken at 88 in FIG. 2;

FIG. 9 is a sectional view similar to FIG. 2 of another embodiment of the control apparatus of this invention illustrating the means for adjusting the minimum valve opening;

FIG. 10 is a partial view similar to FIG. 9 showing a different adjustment of the adjusting means; and

FIG. 11 is a sectional view taken at 11--lll in FIG. 9.

Referring now to the drawings, in FIG. 1 the fluid delivery system of this invention is illustrated as including a pump P of conventional design having a plunger assembly M driven by a prime mover (not shown) and a high pressure fluid end F. Fluid end F has an inlet hose 10 connected to a source of fluid (not shown) and an outlet hose 11. A plurality of nozzle or dump guns, such as two guns G and G illustrated, are generally connected to outlet hose 11, however, according to the present invention two fluid pressure control apparatus 12A and 128 for maintaining a substantially constant load on pump P are connected through hoses l3 and 14 respectively to a Y junction 15 and each of guns G, and G are each connected to the outlets of apparatus 12A and 128 by hoses 16 and 17 respectively through coupling 18. Guns G and G may be any of many designs of dump guns, however, for illustrative purposes they are shown as similar to the gun disclosed in U.S. Pat. application of Amos Pacht, Ser. No. 278,113, filed Aug. 4, 1972, entitled High Pressure Fluid System and Nozzle and Valve Assembly Therefor," and assigned to the assignee of the present application. Guns G and G each include a valve housing 15' having a valve therein, a high pressure nozzle outlet 16 having an orifice 16A (see FIG. 6), a low pressure dump outlet 17', and a handle and trigger mechanism 18' for actuating the valve and directing fluid between either nozzle 16' or dump outlet 17. Guns G, and G typically may be used in high pressure water blasting for cleaning applications, in which case the water pressure at the guns may reach 10,000 psi and over when flow is through nozzle 16', and only several hundred pounds or less when water is dumped. The water pressure at guns G, and G are determined by the size of the orifices 16A in nozzles 116', and the flow rate of pump P.

The details of a preferred form of control apparatus 12A are shown in FIGS. 2 and 3, wherein for purposes of this description only reference will be made to the parts as being up or down (or lower or upper) because of the orientation of FIG. 2. Since apparatus 12A and 12B are identical, only apparatus 12A is shown in FIGS. 2 and 3 and its description will equally apply to apparatus 1213.

As illustrated in FIG. 2, apparatus 12A includes an elongated housing 20 of any suitable cross-section and having a central bore 21 of varying width and circular cross-section through its entire length. Bore 21 includes a relatively large diameter upper portion 22 which terminates at a radially outwardly extending shoulder 23 near the center of housing 20, a relatively narrow intermediate portion 24 between shoulder 23 and a radially outwardly extending shoulder 25 below shoulder 23, and a portion 26 of relatively small diameter extending from shoulder 25 to the lower end of housing 20. Both bore portions 22 and 26 are threaded at their opposite ends as illustrated in FIG. 2, and the threaded part of bore portion 26 extends from the lower end thereof to a shoulder 27 intermediate the ends of portion 26. Also, a threaded inlet passageway 28 is connected for fluid communication to the upper end of bore portion 26.

Central bore portion 26 and inlet passageway 28 together form a flow passageway for the passage of fluid through apparatus 12 and between pump P and gun 6,. A valve means is disposed in this passageway for controlling the flow of fluid therethrough and to provide a substantially constant outlet pressure at pump P irrespective of whether gun G, or G (one or both) is discharging fluid at a high pressure or dumping. For this purpose the preferred form of such valve means includes a cylindrical valve seat member 29 having a central passageway 30 therethrough, an inwardly and downwardly tapered valve seat 31 at its upper end, and an intermediate, outwardly extending threaded portion 32. The lower end 29A of member 29 is enlarged and is internally threaded for coupling to a hose, such as hose 16 through coupling 18, and forms an outlet for the flow passageway through apparatus 12A. Member 29 is screwed into bore portion 26 until threaded portion 32 abuts against shoulder 27 with valve seat 31 extending up into passageway 21 adjacent inlet passageway 28. The upper end of valve seat member 29 includes an O-ring seal 33, illustrated as including an O- ring with a flat backing ring to seal the periphery about member 29 and prevent the flow of fluid between member 29 and the wall of bore portion 26. A valve chamber is thus formed in bore portion 26.

Also extending into this valve chamber from bore portion 24 I is a cylindrical valve stem member 34 adapted to seat at its lower end in a sealing relationship on valve seat 31, and including a lower face 34A. Valve stem member 34 extends through bore portion 24 up into the lower end of bore portion 22, with a close sliding fit, and includes a peripheral O-ring seal 35 having an O-ring and a backing ring, for sealing between the periphery of stem member 34 and the wall of bore portion 24.

Resilient means are provided in bore portion 22 for normally resiliently urging valve stem member 34 under a predetermined force to a closed position where valve stem member 34 is seated on valve seat 31 to close the flow passageway through control apparatus 12A. For this purpose, the resilient means of FIG. 2 includes a coil spring 36 mounted over a cylindrical spring holder 37 which includes a lower retaining circular disk 38 which abuts against the upper end of valve stem member 34. A cylindrical spring retainer plug 39 is threaded into the upper end of bore 211 to close the bore and to provide an upper stop for spring 36 and to urge it under compression against disk 38. Spring holder 37 also includes an upward extending cylindrical guide rod 40 extending through an opening through the center of plug 39 for guiding holder 37, and for providing a tell tale pin to indicate the position of the valve stem member 34. The lower end of plug 39 serves as a stop to limit the upward movement of spring holder 37 to about one-eighth of an inch.

Spring 36 must be large enough to force valve stem member 34 down and thus seat it on valve seat 31 when the water pressure at the outlet of the flow passageway through apparatus 12A is low, i.e., when gun G is dumping, but not so large that the spring cannot be overcome when the pressure in the outlet rises in response to actuation of gun G FIG. 3 illustrates the position of valve stem 34 when the valve is open against the force of spring 36 in response to the fluid pressure at the outlet of apparatus 12A. Also, since plug 39 is threaded the compression of spring 43 can be changed to compensate for pumps of different flow rates and, if needed, the spring can be changed to a stiffer spring. By way of example, if the pressure at outlet 30A is 100 pounds when gun G is dumping, and 5,000 psi or higher when discharge is through its nozzle, spring 43 can be such that pressures of 1,000 pounds or greater at outlet 30A will overcome it. Also, valve stem member 34 and valve seat member 29 are designed as tapered members to provide as little seating surface as possible so that when the valve is seated against high pressure the force of spring 36 required to hold it closed does not have to be excessive. It is also desirable to make the seating area small to increase the size of face 34A in relation to it to provide enough surface area to overcome the force of spring 36.

In order to insure that the load on pump P is substantially constant, apparatus 12A includes means which simulates the effect of high pressure usage by the gun connected thereto even when the gun is dumping. Thus, in so far as the pump is concerned, it sees the same load whether the gun is dumping or not and this would be true where a plurality of guns and control apparatus of this invention are connected to the same pump and operated at random times. In FIG. 2, this means is provided by a passageway 50 and orifice 51 in valve stem 34 which function to provide a flow passageway bypassing the seated valve when the pressure at the outlet of apparatus 12A is low (i.e., gun G is dumping). Passageway 50 passes through the center of valve stem 34 and conducts fluid to orifice 51 which is connected between passageway 50 and face 34A. Orifice 51 (see FIG. 7) is selected to be substantially the size as the nozzle 16' orifice (see FIG. 6) of gun G so that the effect of fiow through the nozzle is simulated when the gun G is dumping.

FIGS. 4 and 5 show an altemat-e arrangement of the means in apparatus 12A for simulating the effect of flow through the nozzle of gun G,. In this case, valve stem 34 includes a stop member, in the form of a circular disk 52 at its upper end, adapted to abut against shoulder 23 and limit the downward movement of stem member 34. The length of stem member 34 is selected so that when it is in its most downward position (see FIG. 4) a slight clearance 53 is provided between the lower end of valve stem member 34 and seat 31 of a size to provide substantially the same restriction to fluid flow as the opening of nozzle 16' does. FIG. 5 shows the open position of the valve of FIG. 4.

FIGS. 9-lll show another embodiment of the control apparatus of this invention in which the valve construction is identical to that of the FIGS. 4 and 5 embodiment, and means is provided for adjusting the size of the minimum clearance through the valve, i.e. the pressure drop across the valve when the nozzle opening of the associated gun is being simulated. As shown in FIG. 9 this adjusting means is preferably provided by a lock nut which is screwed on to threaded portion 32 of valve seat member 29 (the threads of portion 32 extending down to portion 29A in this embodiment) so that when member 29 is screwed into housing 20 nut 60 will be between the lower end of housing 20 and enlarged portion 29A of member 29. In this manner the position of valve seat member 29 in housing 20 can be set and nut 60 then tightened to maintain this position. FIG. 9 shows the nut in position to provide the smallest minimum in opening through the valve 29, 34, and FIG. I0 shows a larger minimum opening with a different setting of valve seat member 29. Since very small differences in the valve opening can result in large changes in pressure drop the adjusting means of FIGS. 9-11 is desirable for providing for fine adjustments of this opening. Also, adjustment can be provided to accommodate for wear of the valve parts occurring when used with high pressures.

In operation in the FIG. 2 embodiment, when gun G is dumping (this description of operation also being applicable to apparatus 128 and gun G so that the pressure at the outlet of apparatus 12A is low, then the valve 29, 34 is closed and flow through the flow passageway 28, 26 is through the by-pass passageway 50 and orifice 51, which as previously noted, is the same size as the orifice in nozzle 16 of gun G Thus, the pressure on the inlet side of valve 29, 34 rises to substantially the same pressure it would be if How were through nozzle 16', and pump P has substantially the same load. However, when trigger 18 in gun G, is activated, to direct water through nozzle 16, the water pressure on the outlet side of orifice 51 also rises to a higher value and water at this higher pressure acts on face 34A and overcomes the force of spring 36 and moves valve stem member 34 up as shown in FIGS. 3 and 5, moving stem 34 off of and out of sealing engagement with valve seat 31. Thus, when trigger mechanism 18 is released and the pressure at the outlet of apparatus 12A is reduced to substantially the dumping pressure of gun G spring 36 will again force valve stem member 34 to close on seat 31. In the embodiment of FIGS. 4, 5 and 9-11, member 34 does not fully close on seat 31 and the desired minimum opening provided when the valve stem member is in its downward position provides the desired pressure drop.

When water is being discharged through the outlet of apparatus 12A, a blast of water will be present and will possibly damage a rubber hose connected to the outlet, such as hose 16. it is thus preferred that some sort of means be connected to the outlet to break up this blast of water before it can damage the connecting hose. One such means is a circular insert member 61 illustrated in FlGS. 2 and 8 which is inserted into the lower end of valve seat member 29 and includes a plurality of holes 62 for breaking up and passing the flow from orifice 51. Another such means (not shown) may be a tube and elbow connected between the outlet and a hose.

Thus, as can be seen from the above description, control apparatus 12A and 12B provide a substantially constant load to pump P and substantially constant inlet pressures for guns G, and G despite the large pressure changes occurring at the guns, which may occur in any sequence during actual use of the guns. This is true whether both guns are dumping, providing a high pressure blast of water, or one is dumping and the other blasting. Also, different size nozzle openings in guns G, and G can be simulated by inserting different valve stems 34 having different size orifices 51, or by adjustment of the minimum opening between seat member 34 and seat 31 when the valve is in its most closed position. Of course, only two guns with two control apparatus are shown, but more than two guns and their respective control apparatus can be provided. Also, by the arrangement shown in FIG. 1, hose 11 can be relatively long and hoses l3 and 14 relatively short to reduce the amount of hosing required with two or more guns located at a substantial distance from pump P.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. In a fluid system for supplying a high pressure stream of fluid, including a pump having a low pressure inlet adapted to be connected to a source of fluid and a high pressure outlet, and at least one nozzle gun having an inlet, a high pressure discharge nozzle, a relatively low pressure dump outlet, and actuating means for diverting flow between said nozzle and said dump outlet, the improvement in said system comprising at least one fluid pressure control apparatus having an inlet adapted to be connected to the outlet of said pump, an outlet adapted to be connected to the inlet of one of said guns, a flow passageway connected between its inlet and outlet, a valve means in said flow passageway responsive to the fluid pressure at said outlet to move between a first position permitting flow through said passageway when the gun connected thereto is actuated to discharge fluid through its nozzle, and to a second position wherein a restriction to flow through said passageway is provided when said gun is dumping, said restriction to flow having substantially the same effect on flow as the restriction to flow provided by the nozzle opening of the gun connected to the outlet of said control means.

2. The system of claim ll wherein said valve means includes a valve seat member and a valve stem member for seating a said valve seat member to close said flow passageway in said second position, and said valve stem member includes an orifice therein for providing said restriction to flow and to by pass said valve means when the valve stem member is seated on said valve stem.

3. The system of claim 1 wherein said valve means includes a valve seat member and a valve stem member, and further including resilient means for urging said valve stem member to be seated on said seat mem ber, and stop means for stopping said valve stem member in the direction of movement towards said valve seat member before seating thereon to provide said flow restriction with said valve stem member in said second position.

41. The system of claim 3 further including adjusting means for adjusting the opening between said value stem member and said seat member when said value stem member is in said second position.

5. The system of claim ll wherein a plurality of nozzle guns are connected to said pump and wherein one of said fluid pressure control apparatus is connected between each such gun and said pump.

6. The system of claim 1 wherein said valve means includes a valve seat member mounted in said flow passageway and an elongated valve stem mounted in said apparatus to extend into said flow passageway for movement between said first position wherein said valve means is open to said second position wherein said valve stem is seated on said valve seat; an orifice in said valve stem adapted to by pass said valve means for fluid flow to provide said restriction to flow when said valve stem is in said second position, and resilient means urging said valve stem into said second position except when the fluid pressure at said outlet exceeds a preselected value.

7. The system of claim 1 wherein said valve means includes a valve seat member and a valve stem member, and further including resilient means for urging said valve stem member towards being seated on said seat member, and means for providing a change in the resilient force urging said valve stem member.

8. The system of claim 1. further including means for breaking up the flow of fluid from said pressure control apparatus.

9. The system of claim 8 wherein said last mentioned means is a disk inserted in to the outlet of said control apparatus said disk having a plurality of flow ports therein.

10. Pressure control apparatus for connection in a high pressure fluid delivery system between a pump and a gun assembly having a high pressure nozzle outlet and a dump outlet, for maintaining a substantially constant load on the pump, said apparatus comprising, in combination: a housing having an inlet adapted to be connected to the outlet of such a pump, an outlet adapted to be connected to such a gun, and a flow passageway connected between said inlet and said outlet; valve means in said passageway for permitting or interrupting flow of fluid from said inlet through said passageway to said outlet, said valve means including means for providing a restriction to fluid flow substantially the same size as the nozzle on said gun, said valve means being responsive to fluid pressure at the outlet of said apparatus to be open to flow when the fluid pressure at said outlet is relatively high; and means for causing said valve means to interrupt flow through said main passageway when the fluid pressure at said outlet is relatively low and divert such flow through said means for providing a restriction to fluid flow.

l l. The apparatus of claim Ml wherein said means for 10 justing means for adjusting the minimum opening through said valve means.

l l 1 l t 

1. In a fluid system for supplying a high pressure stream of fluid, including a pump having a low pressure inlet adapted to be connected to a source of fluid and a high pressure outlet, and at least one nozzle gun having an inlet, a high pressure discharge nozzle, a relatively low pressure dump outlet, and actuating means for diverting flow between said nozzle and said dump outlet, the improvement in said system comprising at least one fluid pressure control apparatus having an inlet adapted to be connected to the outlet of said pump, an outlet adapted to be connected to the inlet of one of said guns, a flow passageway connected between its inlet and outlet, a valve means in said flow passageway responsive to the fluid pressure at said outlet to move between a first position permitting flow through said passageway when the gun connected thereto is actuated to discharge fluid through its nozzle, and to a second position wherein a restriction to flow through said passageway is provided when said gun is dumping, said restriction to flow having substantially the same effect on flow as the restriction to flow provided by the nozzle opening of the gun connected to the outlet of said control means.
 2. The system of claim 1 wherein said valve means includes a valve seat member and a valve stem member for seating a said valve seat member to close said flow passageway in said second position, and said valve stem member includes an orifice therein for providing said restriction to flow and to by pass said valve means when the valve stem member is seated on said valve stem.
 3. The system of claim 1 wherein said valve means includes a valve seat member and a valve stem member, and further including resilient means for urging said valve stem member to be seated on said seat member, and stop means for stopping said valve stem member in the direction of movement towards said valve seat member before seating thereon to provide said flow restriction with said valve stem member in said second position.
 4. The system of claim 3 further including adjusting means for adjusting the opening between said value stem member and said seat member when said value stem member is in said second position.
 5. The system of claim 1 wherein a plurality of nozzle guns are connected to said pump and wherein one of said fluid pressure control apparatus is connected between each such gun and said pump.
 6. The system of claim 1 wherein said valve means includes a valve seat member mounted in said flow passageway and an elongated valve stem mounted in said apparatus to extend into said flow passageway for movement between said first position wherein said valve means is open to said second position wherein said valve stem is seated on said valve seat; an orifice in said valve stem adapted to by pass said valve means for fluid flow to provide said restriction to flow when said valve stem is in said second position, and resilient means urging said valve stem into said second position except when the fluid pressure at said outlet exceeds a preselected value.
 7. The system of claim 1 wherein said valve means includes a valve seat member and a valve stem member, and further including resilient means for urging said valve stem Member towards being seated on said seat member, and means for providing a change in the resilient force urging said valve stem member.
 8. The system of claim 1 further including means for breaking up the flow of fluid from said pressure control apparatus.
 9. The system of claim 8 wherein said last mentioned means is a disk inserted in to the outlet of said control apparatus said disk having a plurality of flow ports therein.
 10. Pressure control apparatus for connection in a high pressure fluid delivery system between a pump and a gun assembly having a high pressure nozzle outlet and a dump outlet, for maintaining a substantially constant load on the pump, said apparatus comprising, in combination: a housing having an inlet adapted to be connected to the outlet of such a pump, an outlet adapted to be connected to such a gun, and a flow passageway connected between said inlet and said outlet; valve means in said passageway for permitting or interrupting flow of fluid from said inlet through said passageway to said outlet, said valve means including means for providing a restriction to fluid flow substantially the same size as the nozzle on said gun, said valve means being responsive to fluid pressure at the outlet of said apparatus to be open to flow when the fluid pressure at said outlet is relatively high; and means for causing said valve means to interrupt flow through said main passageway when the fluid pressure at said outlet is relatively low and divert such flow through said means for providing a restriction to fluid flow.
 11. The apparatus of claim 10 wherein said means for providing said restriction to fluid flow is an orifice in said valve means through which fluid can by pass said valve means when closed.
 12. The apparatus of claim 10 wherein said valve means further includes stop means for preventing full closure of said valve means to provide said means for providing said restriction to fluid flow.
 13. The apparatus of claim 12 further including adjusting means for adjusting the minimum opening through said valve means. 